Products having electrically driven heating features are prevalent. Such products can be found in cars, homes, and offices. Many such heaters require that they quickly reach a requested or preset target temperature but do not significantly exceed the temperature. It is commonly expected that heating devices are safe, especially for personal consumer products.
Various methods are currently utilized in an attempt to achieve the requisite levels of safety and performance. For example, many kitchen appliances, such as kettles, cooking plates, irons, and coffee makers, use thermal fuses or circuit breakers. Due to their relatively large size, thermal fuses or circuit breakers are typically used in products of sufficient size to house these electrical components without detracting from the desired form factor of the product.
Another approach to increase the safety of a heating device is to use control circuitry for temperature regulation, with the control circuitry using an input from a temperature sensor. However, in case of a failure of the control circuit and/or the temperature sensor, the heating element may undesirably experience excessive heating. Yet another approach to increasing the safety of heating devices is to control the generated heat through the use of self-limiting heating elements that have a positive temperature characteristic, sometimes referred to as “PTCs,” which increase in electrical resistance as temperature increases. Thus, a PTC is self-limiting at a certain temperature since, when driven by a constant voltage source (e.g., a battery), the temperature stabilizes at a certain value because the supplied power (P=V2/R) decreases with the increasing temperature until it is in balance with the dissipated power. This technique can be used, for example, for a heated car mirror, certain hair stylers, and other household appliances. However, even though PTC-based devices are self-limiting, they can undesirably take a relatively long period of time to reach the steady state temperature, as providing power to the PTC element slows down as it comes closer to the steady state temperature.
Thus, it would be advantageous to provide for a product with heating features that addresses one or more of these issues. Indeed, it would be advantageous to provide for a personal consumer product that provides sufficient heating levels within a desired period of time while maintaining a desired form factor for its use. It would also be advantageous to provide a personal consumer product having circuitry that prevents overheating. It would further be advantageous to provide a diagnostics routine to test the operation of hardware and software of the personal consumer product.